This invention relates to a lock with key slot manipulation barrier therein and more particularly, to a rotatable lock plug having a key slot formed axially therethrough wherein a barrier is positioned secured in the lock plug at an inner end of the lock plug effectively blocking the key slot against surreptitious attempted manipulation therethrough and manipulation of the various connected components controlled by the lock. Even more particularly, this invention relates to a lock plug having the key slot guarding barrier of the foregoing general character wherein the barrier is specifically and uniquely formed adapted to occupy a minimum of lock plug axial space directly at the effective working area of the key slot so as to minimize the required axial length of the particular lock plug, yet the barrier is securely retained in its blocking position and efficiently serves its required key slot blocking function.
The use of so-called "armor pins," that is, hardened cylindrical pins, as shields or barriers in locks for guarding various of the important lock components has been well known to those skilled in the lock art for a lengthy period of time. For instance, particularly before the improved and more sophisticated metals of today and the methods of working the same were available, lock security could be violated by drilling through exposed parts thereof into the inner lock confines for gaining manipulative access to the various lock working elements. Barriers were therefore installed, a somewhat common form being in the pin-tumbler locks wherein an armor pin would be installed in the lock plug positioned directly forward of the first pin-tumbler to protect the pin-tumblers from such drilling access and ultimate manipulation.
Although the improvement and progress in the lock arts and the availability of improved metals temporarily eliminated the necessity of the increased guarding of the various lock elements so that the use of armor pins was, in most cases, eliminated, changes in lock production procedures for time and cost savings ultimately required a rethinking of the lock guarding structures. A major change was the formation of the key slots of the lock plugs totally axially therethrough with the usual radially extending levers secured to the lock plug inner ends, usually adjacent the open key slot inner end. In any event, with the key removed, the open key slot provided access through the key slot inner end and access to either the lock plug connected lever or to the various elements controlled by the lock.
Thus, armor pins were once again used to deny drilling and other penetrating access through the open key slots. This was done merely by drilling a cylindrical hole aligned with the key slot adjacent the lock plug inner end and installing a press fit armor pin totally blocking the key slot. Of course, the armor pin was required to be positioned across the key slot axially inward of the usual penetration by the proper key when inserted in the key slot.
Still in more recent years, the lock art has progressed to the use of torque blades in one form or another for connecting the lock plug to the particular elements or mechanisms controlled thereby, frequently door bolt mechanisms. Furthermore, the torque blades are attached to the lock plugs through lost motion connections so that the lock key is always removable in a common neutral position. In other words, with the lock plug and inter-connected bolt mechanism connected through the torque blade and lost motion connection of the torque blade to the lock plug inner end, turning of the key in one direction will extend the bolt and the key may be returned to its neutral position through lost motion not affecting the position of the bolt, the withdrawal of the bolt being similar, but in the opposite direction of key movement.
One general construction of lock and bolt mechanism assembly exemplifying this arrangement includes the lock plug having the key slot formed axially therethrough, an axially extending torque blade, and one end of the torque blade lost motion connected to the lock plug inner end and the other end of the torque blade secured with the bolt mechanism for actuating the same to move the bolt. The lost motion connection between the torque blade and the lock plug inner end is created by either inserting the torque blade end into an end-opening recess of the lock plug or telescoping the torque blade end over the lock plug end, in either case, connecting the lock plug and torque blade for rotation transmission therebetween through a slot and pin arrangement providing the limited lost motion. The important consideration is that with the torque blade end, whether recess received or telescoped with the lock plug end, the inner open end of the key slot is completely covered and thereby obstructed by the torque blade so that the torque blade prevents any manipulation through the key slot and the barrier created by armor pins is unnecessary. Thus, the armor pin was again eliminated.
Although this more recent torque blade and lock arrangement has appeared to provide sufficient key slot access blocking for frustrating attempted manipulations, with the more sophistication and adeptness of the criminal element attempting to surreptitiously manipulate the locks, it has been determined that some form of the prior static or absolute blocking of the key slot will provide added assurance that complete key slot access blocking is maintained, for instance, similar to the cylindrical armor pin blocking of the prior locks. However, with the lost motion connection between the lock plug and torque blade ends occupying an increment of the lock plug inner end portion, a distinct problem is presented. That problem is one of lock plug axial space, the space required for positioning a cylindrical armor pin at the inner end of the key slot while still not interfering with the key outwardly thereof and the lost motion connection inwardly thereof.
If the lock is to have the maximum number of pin-tumblers and such pin-tumblers are of sufficient size, all for the required maximum locking security, the key must be of a determined axial length. This means that the key, when in proper unlocking position received in the lock plug key slot will occupy all but a very small inner axial portion of the lock plug. Thus, it has been found that there simply is not sufficient axial length of the lock plug remaining between the key inner end when properly positioned in the key slot and the torque blade lost motion connection at the lock plug inner end portion to install a normal cylindrical armor pin in the lock plug of sufficient size as had heretofore been used for fully blocking the key slot and being securely retained in such blocking position, that is, without increasing the lock plug axial length and, therefore, the overall lock dimensions, which can cause serious prohibitive problems in lock installation, as well as increased lock costs.
In an effort to solve this problem of providing adequate key slot blocking while still maintaining the required lock plug length and other component sizes, various attempts have been made to provide some form of shield of altered shape from the prior fully cylindrical armor pin occupying the very limited axial space of the lock plug between the key inner end and the torque blade lost motion connection to the lock plug. These attempts have involved the lost motion connection between the lock plug inner end and the end of the torque blade being formed by the inwardly opening, axial recess in the lock plug inner end receiving the torque blade end therein. Flat plates or cup-shaped members have been press fit with a maximum possible compression in the lock plug lost motion recess fully blocking the key slot outwardly of the torque blade end, but these attempts fail due to the fact that it is found to be impossible to provide sufficient press fit compression between these shields and the lock plug to prevent the shields being dislodged by an adequate punch inserted fully into the key slot from the outer end when the key is not present.